I think you will find the losses in the alternator itself are greater than fractions of a hp. Under full load, the alternator could be consuming several hp just to build the magnetic field in it's coils.

There is no free lunch

Right, but the portion of that that is due to the fan is a fraction of a horsepower ;-)
13.6 volts * 90 amps is about 1.6 horsepower.

A trip over to wikipedia sites a source saying that car alternators have an efficiency between 50% and 62%.
So worst case an alternator will eat 3.2hp, plus other resistance associated with the pulley system.

Does this sound about right?

Pretty bad conversion rate there for energy, aye?

~Tyler

edit* of course 3.2hp is only if the alternator is rated for 90amps, and it is attached to something drawing all 90 amps. I doubt our cars use close to 90 amps in normal operation, at least not if the battery is charged.

There are some good reasons to use an electric fan, like in the case of FWD vehicles with their engines placed sideways in the engine compartment. But even in our E30s, if it is a/c equipped it will have an auxiliary electric fan placed ahead of the a/c condenser ahead of the radiator. That electric fan should come on automatically whenever the a/c is engaged, or whenever the coolant temp exceeds a certain level.

Even though there undeniably are efficiency losses in converting gasoline to mechanical energy to driving an alternator to create electricity to then reconvert the electricity back to mechanical energy via the electric motor to drive the auxiliary fan, it's much simpler than trying to rig a complicated mechanical drive around or through the radiator.

There are other ways that an electric drive is more desirable, regardless of the efficiency losses, such as in diesel locomotives. Huge diesel engines power the locomotive, but the problem is that piston engines will only make useful torque and power at some non-zero rpm. They can't pull anything from a standstill without slipping a clutch somewhere in the driveline. If you're trying to pull a heavily loaded train from a standstill, you're going to be burning clutches something fierce.

So, instead the locomotive uses the powerful diesel engine to drive a generator that powers an electric motor to pull the train. Electric motors are ideally suited for this purpose because they create maximum torque from a standstill and don't require a clutch.

Hybrid gasoline/electric motors are more efficient at using fuel only because the gasoline engine can be run constantly at its optimum fuel efficient rpm, rather than constantly varying engine speed up and down through different gears, to charge a battery or run a generator that in turn powers an electric motor to drive the vehicle.

The biggest fuel efficiency benefit though is in using the electric motor in reverse to put a big load on it to charge the battery in regenerative braking. Rather than just burning up the car's kinetic energy in heating the brake rotors, that energy is put to use instead recharging the battery. The torque required to turn the motors into generators is used to slow the car.

In big diesel locomotives they also use the electric drive motors as brakes, simply by using the motors as generators to drive current through huge resistors, "waffle plates", that glow red hot. It requires enormous brake torque to pump the current that causes those waffle plates to glow hot. In that way they convert the kinetic energy of the train into heat which is dumped to the atmosphere.

A trip over to wikipedia sites a source saying that car alternators have an efficiency between 50% and 62%.
So worst case an alternator will eat 3.2hp, plus other resistance associated with the pulley system.

What about the efficiency of an electric motor of the size required to run the fan? I looked up the v-belt efficiency and I asked you about the electric motor efficiency way back at the beginning of this this thread. You're the electrical engineering student, so I thought you might have that info handy. I'm the mechanical engineer, so I took care of the v-belt. Ferd is obviously the saintly teacher because nobody but a Saint or a teacher would have the patience to explain something as many times as he has in this thread. Good explanations too. Anyway, what's the efficiency of that motor?

A trip over to wikipedia sites a source saying that car alternators have an efficiency between 50% and 62%.
So worst case an alternator will eat 3.2hp, plus other resistance associated with the pulley system.

What about the efficiency of an electric motor of the size required to run the fan? I looked up the v-belt efficiency and I asked you about the electric motor efficiency way back at the beginning of this this thread. You're the electrical engineering student, so I thought you might have that info handy. I'm the mechanical engineer, so I took care of the v-belt. Ferd is obviously the saintly teacher because nobody but a Saint or a teacher would have the patience to explain something as many times as he has in this thread. Good explanations too. Anyway, what's the efficiency of that motor?

John

Humm. I'm a computer science graduate, not an electrical engineer student. I'd love to graphically model and run calculations on this electrical magic using software, if you provide me with an electrical engineer
If you asked ME specifically about efficiencies, my apologies for missing that question. However, I've never studied this matter, and did not known until I went looking around the internet for it. I took some basic physics classes, so I'm well aware of the laws of conservation of energy, and myths of perpetual motion machines etc etc. But I certainly never studied applications of these laws past 60 second examples.

Ferd is quite informative, and if I might say, very good at getting information across in a written format.

Humm. I'm a computer science graduate, not an electrical engineer student. I'd love to graphically model and run calculations on this electrical magic using software, if you provide me with an electrical engineer
If you asked ME specifically about efficiencies, my apologies for missing that question.

Oh, sorry. I didn't mean to insult you like that. I thought I remembered something about EE from a while ago, but I was obviously mistaken.

I didn't really ask you specifically, but since I was operating under the misconception that you had been studying EE, I though bringing it up would remind you about all the efficiency related EE problems you had been solving in the engineering courses you weren't taking. (Did you follow that? It was confusing to type - maybe it's the beer).

I'm having IPA I made that's loaded with hops from the PNW.

Oh yeah, electric motors are about 95% efficient. V-belts are equal to or better than that when they're adjusted right, but probably not as good if the belt is slipping. Then you have the conversion to electric and back to rotation with the motor, but surely we all know that by now.

Humm. I'm a computer science graduate, not an electrical engineer student. I'd love to graphically model and run calculations on this electrical magic using software, if you provide me with an electrical engineer
If you asked ME specifically about efficiencies, my apologies for missing that question.

Oh, sorry. I didn't mean to insult you like that. I thought I remembered something about EE from a while ago, but I was obviously mistaken.

I didn't really ask you specifically, but since I was operating under the misconception that you had been studying EE, I though bringing it up would remind you about all the efficiency related EE problems you had been solving in the engineering courses you weren't taking. (Did you follow that? It was confusing to type - maybe it's the beer).

I'm having IPA I made that's loaded with hops from the PNW.

Oh yeah, electric motors are about 95% efficient. V-belts are equal to or better than that when they're adjusted right, but probably not as good if the belt is slipping. Then you have the conversion to electric and back to rotation with the motor, but surely we all know that by now.

John

Apology accepted, and I understand what you're saying despite what is surely an amazing IPA

So for anyone who comes across this thread later, I think I can sum up what our collective musings have determined.
(Ferd may feel free to reword anything in a more eloquent many if he sees fit)

The mechanical belt systems operate at about 90% efficiency, where as an electric motor operates at about 95% efficiency.
Seemingly making an electric motor solution more energy effective.
However, there is a 50-62% loss of energy in the alternator in transforming the mechanical energy to electrical energy.

Until we can produce an alternator with better than 95% efficiency, an electrical fan will not put more horses to the wheels.
However as noted by Ferd, there are many good reasons to use an electric motor, just none of them have to do with being more energy efficient, but are based in practicality.

QuoteEarendilThe mechanical belt systems operate at about 90% efficiency, where as an electric motor operates at about 95% efficiency.
Seemingly making an electric motor solution more energy effective.
However, there is a 50-62% loss of energy in the alternator in transforming the mechanical energy to electrical energy.

Until we can produce an alternator with better than 95% efficiency, an electrical fan will not put more horses to the wheels.
However as noted by Ferd, there are many good reasons to use an electric motor, just none of them have to do with being more energy efficient, but are based in practicality.

Did I miss anything or misrepresent anything?

Just one thing to add. Yes, an electric motor probably does operate more efficiently than a mechanical belt system. But obviously one gains nothing by still using the same mechanical belt system to drive an alternator to power the electric motor. In that case it makes more sense to use the belt system directly.

An electric motor is certainly a better mechanism for driving things, but you need to consider how and where the energy is coming from to provide the required electricity, It's much the same case that's being made to promote the use of hydrogen as a miracle fuel to save the planet. There's no arguing that hydrogen burns cleaner than fossil fuels, producing nothing but clean energy and water as byproducts. It's practically miraculous.

However, hydrogen is not an energy "source". It, like pretty much any other fuel, is merely an energy "storage" medium. Hydrogen does not grow for free on trees, and contrary to popular belief, hydrogen does not lie idly in every lake and ocean waiting to be poured straight into your fuel tank. No matter how attractive hydrogen is as a fuel, it doesn't come for free.

Every school kid knows that hydrogen can be produced by electrolysis, splitting water into hydrogen and oxygen. From there, gullible people can easily be led to believe that the oceans will provide an endless supply of hydrogen. However, the electrolysis process consumes more energy to split the hydrogen from water than can be usefully recovered later in burning the hydrogen to power your homes and cars. The energy to drive the electrolysis process has to come from somewhere. You've gained nothing if you're burning fossil fuels in a power station to generate the electricity necessary to power the electrolysis process to provide hydrogen to heat your home. It is far more efficient to bring the fossil fuels directly to your furnace.

Currently, by far the cheapest and most plentiful source of hydrogen is natural gas. Burning more natural gas even provides the power required to strip the hydrogen out of this abundant hydrocarbon fuel. However, at the end of the process you're left with an amount of hydrogen containing less than 50% of the energy that was contained in the original amount of natural gas. Where's the sense in that? Why not just use the natural gas directly?

Strictly speaking, not even hydrocarbon fuels are an energy "source". They were originally plant and animal matter that died, then collected in sufficient quantities under the right conditions to cook for millions of years and eventually form pools of oil. Those plants and animals fed off each other, all ultimately fuelled by the weak energy cast on them by the far away sun. In effect, all hydrocarbon fuels are an energy "storage" medium for condensed, collected, and highly concentrated -- sunlight!

We will continue to tout miracle fuels like hydrogen or bio-fuels or hybrids, simply because we still can. But, as we ever more rapidly consume the easily harvested reservoirs of energy-dense petroleum products, very soon we will eventually need to find ways to capture energy more efficiently directly from the sun.

QuoteFerdinand
We will continue to tout miracle fuels like hydrogen or bio-fuels or hybrids, simply because we still can. But, as we ever more rapidly consume the easily harvested reservoirs of energy-dense petroleum products, very soon we will eventually need to find ways to capture energy more efficiently directly from the sun.

Or mimic the sun by going nuclear!

Energy-dense petroleum products are only an advantage when the energy source needs to be portable, such as vehicles. So far we haven't been able to capture solar energy (solar panels) directly to the moving device in sufficient quantity for that to be practical or to satisfy performance requirements. But that could come!

The mechanical belt systems operate at about 90% efficiency, where as an electric motor operates at about 95% efficiency.
Seemingly making an electric motor solution more energy effective.
However, there is a 50-62% loss of energy in the alternator in transforming the mechanical energy to electrical energy.

Until we can produce an alternator with better than 95% efficiency, an electrical fan will not put more horses to the wheels.
However as noted by Ferd, there are many good reasons to use an electric motor, just none of them have to do with being more energy efficient, but are based in practicality.

Did I miss anything or misrepresent anything?

This is all very well, but nobody went into this: WHEN is the energy used.

The fan is an auxiliary method to cool the radiator only when the car is stopped, or moving slowly.
Then, you are not very concerned about that little amount of power, cause you have the engine idling anyway.
When the car is moving at speed, or starting from completely cold, the electric fan is completely shut off, while the mechanical one keeps going. Thats why BMW introduced the fan clutch, to save some power by slipping and letting the fan run slower than it would if directly driven by the pulley. sadly, the fan clutch is the weak link, it will eventually fail and be replaced several times through the car useful life.

As for electric fans, those are operated by a thermostat switch mounted somewhere on the radiator or thermostat casing, it monitors the water temperature and turns the fan on and off automatically. Can't think why anyone would want a manual override...
Eventually it may fail, it will probably be the thermostat which is rather inexpensive and easy to replace.
As for the electric power needed, your car has an alternator turning anyway, so the extra resistance needed to produce a little extra power for the fan is about the same either way, at the alternator belt or at the fan clutch.

The mechanical belt systems operate at about 90% efficiency, where as an electric motor operates at about 95% efficiency.
Seemingly making an electric motor solution more energy effective.
However, there is a 50-62% loss of energy in the alternator in transforming the mechanical energy to electrical energy.

Until we can produce an alternator with better than 95% efficiency, an electrical fan will not put more horses to the wheels.
However as noted by Ferd, there are many good reasons to use an electric motor, just none of them have to do with being more energy efficient, but are based in practicality.

Did I miss anything or misrepresent anything?

This is all very well, but nobody went into this: WHEN is the energy used.

The fan is an auxiliary method to cool the radiator only when the car is stopped, or moving slowly.
Then, you are not very concerned about that little amount of power, cause you have the engine idling anyway.
When the car is moving at speed, or starting from completely cold, the electric fan is completely shut off, while the mechanical one keeps going. Thats why BMW introduced the fan clutch, to save some power by slipping and letting the fan run slower than it would if directly driven by the pulley. sadly, the fan clutch is the weak link, it will eventually fail and be replaced several times through the car useful life.

As for electric fans, those are operated by a thermostat switch mounted somewhere on the radiator or thermostat casing, it monitors the water temperature and turns the fan on and off automatically. Can't think why anyone would want a manual override...
Eventually it may fail, it will probably be the thermostat which is rather inexpensive and easy to replace.
As for the electric power needed, your car has an alternator turning anyway, so the extra resistance needed to produce a little extra power for the fan is about the same either way, at the alternator belt or at the fan clutch.

Good point about when the energy is used

But there can be considerable energy draw from the alternator when the fan does turn on. The fan always operates at it's maximum designed speed and as has been pointed out, this will consume more than a little power.

The mechanical fan, thru the clutch, will use varying amounts of energy from the engine as it slips more or less depending on the temperature.

In the end, it's hard to say which system uses more energy but I suspect it is still going to be the electric fan

QuoteIn the end, it's hard to say which system uses more energy but I suspect it is still going to be the electric fan

Now thats an easy one.
The electrical fan can be set up to work in two speeds, half speed at a given temperature range, and full speed above certain temperature, shut off when not needed.
Power consumption for electric fan would be P (fan power) * time at full speed, P/2 * time at low speed, 0 when shut off.
Power consumption for fan clutch is P*(clutch factor) , where the clutch factor ranges from a low value, when fan is unneeded but is turning at slow speed, and near one, when all temperature is hot and the clutch engages completely.
P should be the same or similar for either fan, the power needed to move enough air to the radiator.
I suspect the fact that fan clutch is always turning, while electric fan is stopped most time, and seldom goes to high speed, offsets the advantage of the fewer energy transformations for the engine driven fan.
Now we only need to put figures on that "clutch function" over temperature and time to compare.

We had well established the difference in power consumption is very slim, and both setups are very reliable and simple enough.

QuoteIn the end, it's hard to say which system uses more energy but I suspect it is still going to be the electric fan

Now thats an easy one.
The electrical fan can be set up to work in two speeds, half speed at a given temperature range, and full speed above certain temperature, shut off when not needed.
Power consumption for electric fan would be P (fan power) * time at full speed, P/2 * time at low speed, 0 when shut off.
Power consumption for fan clutch is P*(clutch factor) , where the clutch factor ranges from a low value, when fan is unneeded but is turning at slow speed, and near one, when all temperature is hot and the clutch engages completely.
P should be the same or similar for either fan, the power needed to move enough air to the radiator.
I suspect the fact that fan clutch is always turning, while electric fan is stopped most time, and seldom goes to high speed, offsets the advantage of the fewer energy transformations for the engine driven fan.
Now we only need to put figures on that "clutch function" over temperature and time to compare.

We had well established the difference in power consumption is very slim, and both setups are very reliable and simple enough.

Without actual measured energy consumption of both systems, we can only make educated guesses.

I wonder if we could offset the power used by the electric fan if we had it generate electricity when it isn't being driven for cooling? Just set it up like the regenerative braking system in electric/hybrid cars. That would make it way more efficient than the mechanical fan which cannot produce anything but drag

QuoteWithout actual measured energy consumption of both systems, we can only make educated guesses.

Nope, it can be calculated. Where is Vlad Amuzescu when you need him?!

For the electric fan, see above, just multiply time on and power, thats the energy consumed. Then multiply by th efficiency of the alternator, and you get how much energy (KWh) was taken from the crankshaft to cool the engine, over a given period of time.

The bold is mine, is the interesting data.
So, as i suspected, the fan is always on, and it cant slip less than 70%, or more than 20%, at best. (lets assume 25%-65%).
Plus, from my reading, if the 65% slippage must draw enough air (car idling, 750rpm), then when you go at 6000 rpm (and you want to do that occasionally ) and you get the minimum slippage, which is 25%, way more than needed to cool the radiator.
That means waste of power when you need it most, to pass that electrical fan cooled Honda crawling uphill in front of your fine car.
Not to mention when you go fast and don't need the fan at all, it still draws those 25% from the crankshaft, always.

So, back to the original point: the best setup depends on what you want to do with the car.

Amazing, so much discussion about something hardly needed. My son's E-36 has no fan at all and does not over heat even on a track day. I had a E-30 318 that had a little front damage so removed the fan to keep it out of the radiator. It would only overheat if setting several minutes idling in the drive through line. In normal traffic it was fine. My E-30 325 has a very worn fan clutch that barley turns the fan above an idle speed and it never overheats. The electric fan for the AC never goes on high speed and only runs when the AC is turned on. Even idling in traffic on a hot day barely got past the middle of the temp gage. If one needs to run AC in stop and go traffic there has to be a fan to make the AC work for sure and standing at idle for more than a few minutes will cause a car to overheat. If someone was going up a steep hill at low speed, might wish for a fan that could be turned on as needed.

One benefit I see of an electric fan is that it is less likely one will put a finger into it.

My grandmother has a Lexus with (believe it or not) a hydraulic driven fan. The power steering pump powers the fan when the temp sensor tells it to. Even at idle, it really spins. Setting at idle in the driveway, it will cycle on and off every couple minutes. While driving, without AC it probably never comes on.

QuoteBob in Everett
Amazing, so much discussion about something hardly needed.

Bob in Everett

Hey, if you can't spend hours on the internet discussing (or arguing about) things that don't matter, then what's it good for?

John

Trolling?

Same thing?

I have a few friends who enjoy sitting around with me and discussing/hypothasizing about things we only partially understand. I think it's something humanity could use a lot more of, as humans are generally able to figure a lot of stuff out, if they try for longer than 30 seconds

Though, I once had a room mate that when engaging in these sorts of discussions always started taking it personally and would get upset if I didn't agree with him in a relatively short period of time. I kept things superficial after a while

The difference I see is that trolling is intended to cause trouble and what we've been doing with the electric motor and A/C threads (and others like them) is dig into the details of things that most people wouldn't be interested in.

Thread hijacking is when somebody changes the subject and heads off in another direction. Maybe even discussing something that should be on another forum. I sure wouldn't do that!

Ok, so maybe I sound like an old curmudgeon. Just seems like something as reliable as a mechanical fan would not be replaced by a bunch of complex electrical stuff that is more likely to cause a problem.

My primary job is designing hydraulic equipment and someone is always trying to replace some if with an electric gizmo that costs more and weighs more. The only advantage is that when the non-hydraulic thing leaks, the leak is a lot harder to find.

I have been out and about for most of the later months of the summer just came back to the real world hopped on. My surprise to see a question I asked months ago is still up at it. Hope everyone had a good and productive summer. And yes I will be taking out my fan and installing a slimmer electric fan, will report on how it FEELS. No imperial evidence here.

Quotejl1371
I have been out and about for most of the later months of the summer just came back to the real world hopped on. My surprise to see a question I asked months ago is still up at it. Hope everyone had a good and productive summer. And yes I will be taking out my fan and installing a slimmer electric fan, will report on how it FEELS. No imperial evidence here.

Well the thread was fun and educational, but I don't remember if we ever all agreed. What I think we did agree on is that the difference is a fraction of a hp. So when it comes to rubber on the road, you should only notice a placebo effect